The most common overrunning roller clutch is the type in which a roller retaining cage is anchored to the cam race. The cage includes a series of box shaped pockets, each of which contains a cylindrical roller and an accordion energizing spring. Each pocket sits over the longer leg of a V-shaped notch, the so-called cam ramp. The energizing springs push off of the fixed cage to keep each roller pushed into constant light contact with both the cam ramp and the pathway race. Each spring can rapidly and independently expand and contract to keep its roller in this lockup ready position, thereby compensating for any running eccentricity between the races. Since each cage pocket must be wide enough to carry a roller and spring, the number of rollers that can be incorporated is limited.
In another, less common, type of roller clutch, the cage is not anchored to the cam race, but is instead twisted relative to the cam race in order to force all of the rollers at once in one direction or the other along the cam ramps, so-called "cage phasing". Occasionally, the cage is actively twisted by an external actuator, such as a piston. More often, the cage is passively twisted by an internal drag means, such as drag springs, that ride between the pathway race and the cage. Typically, in a passively actuated cage phased roller clutch, each pocket contains only a roller, so that a greater number of rollers can be incorporated. In operation, one edge of each roller pocket pushes a respective roller toward lockup position. When the races shift to free running mode, the drag spring twists the cage in the opposite direction, carrying the rollers down the cam races toward the cam hooks, so that they cannot wedge between the races.
There are shortcomings in the conventional passively actuated cage phased roller clutch design. The rollers cannot be fitted tightly between the edges of the roller pockets without retarding their rolling, so there is some pocket edge-roller play. Furthermore, manufacturing tolerances in the cage mean that the pocket edge spacing differs from pocket to pocket, as does the roller-pocket edge play. The position of the roller during overrun, its lockup ready position, is determined only by the loose confinement of the rollers in its pocket. With nothing to compensate, the cage may not shift all the rollers simultaneously and evenly. Nor is there anything to cushion the pocket edges from direct collision with the rollers when they do shift. Also, during overrun, the rollers can rub on the relatively rotating pathway, though this is true of most cam carried roller clutches, as well. The lack of individual energizing springs also means there is nothing to retain the rollers in the cage pockets before the cage is installed between the clutch races, making installation more difficult.